Below are some guidelines to follow when fitting a Comfort Classic mask. Landmarks a.) Sides of nostrils b.) Bridge of nose zone c.) Below the nose tip, above the lip 1. Begin with the sizing gauge. (Link below) 2. Check landmarks. 3. Choose the smallest mask that fits without pinching or obstructing the nostrils. 4. Tighten top straps of headgear, then bottom. Do NOT over tighten straps. 5. Try the mask on with the unit at the prescribed pressure to ensure proper fit. Download Comfort Classic Sizing Gauge